Man has become more dependent on portable technology in all arenas of life from business, to medicine, to recreation, to first response/disaster relief, to exploration, to field scientists, and to the military. This dependence requires electricity, which is presently provided by batteries. Total dependence on batteries is problematic as people working off the electric grid may have to carry up to 25 lbs of batteries. A device that could generate significant electrical energy to recharge batteries would provide much more freedom and operational ability.
Until recently, electrical energy harvesting from body movements has been extremely limited in terms of wattage (10 or 20 milliwatts). The present inventor has previously disclosed a backpack device which can generate electricity when carrying very heavy loads (U.S. Pat. No. 6,982,497 “A Backpack for Harvesting Electrical Energy During Walking and for Minimizing Shoulder Strain”). That device suspends the load so that it operates as a force-damped oscillator that generates electricity from a geared generator via a rack and pinion arrangement. The description in U.S. Pat. No. 6,982,497 is hereby incorporated by reference.
Exemplary applications of such a power generating backpack include backpacks for soldiers. Combat units operating on foot in remote regions are highly dependent on electrical energy for communications, navigation and sensing. As the use of electronic devices on the battlefield has increased, so has the need for electrical energy independence. At present, power is provided by carrying a large weight of batteries (as much as 20 lbs), which when added to their usual 801b packs, represents a crushing burden, resulting in reduced performance and back/joint injuries for the soldiers. The electricity-generating backpack described in U.S. Pat. No. 6,982,497 addresses this problem by providing significant levels of electricity generation from human movement. For example, during normal walking, the backpack originally generated over 2 watts of electricity and was later modified to generate up to 7.5 watts of electricity. This is significantly more energy than previous devices. At the same time, the backpack provides ergonomic benefits as the soldiers walk. This electricity production will permit soldiers to replace up to 20 lbs of disposable batteries with a small rechargeable battery.
Use of backpacks of the type described in U.S. Pat. No. 6,982,497 will permit longer and better performance in the field by combat soldiers and special forces. The backpack will enable military units to go into the field and essentially generate their own electrical power as they need it. This will permit them to stay longer in the field, and because they will not need to carry 20 lbs of batteries, the soldiers will be more mobile. Further, because of the reduction in forces on the body, the soldier will be able to move faster (i.e., run) than they can presently, with an expected reduction in orthopedic injury. Hence, use of the ergonomic backpacks described in U.S. Pat. No. 6,982,497 is expected to lead to not only lower incidence of orthopedic injury during deployment, but also fewer orthopedic problems following deployment and in later years. Finally, at present Marines use disposable batteries because of their higher energy density. The 1 kg batteries used presently cost $70-90 each and Marines may use 1 or 2 a day that are disposed of after use. The electricity generating backpack of U.S. Pat. No. 6,982,497 will greatly reduce this recurring battery cost and reduce the environmental cost of manufacturing and disposing of millions of lithium-ion batteries. Such a backpack will also save considerable funds by generating the electricity for free.
However, there are a number of limitations that limit the practical use of the backpack of U.S. Pat. No. 6,982,497. For example, a significant limitation involves the necessity for damping of the mechanical dynamics and hence the need for appropriate management of energy drawn from the mechanical system by the generator. The backpack also has several other limitations including: 1) it is very heavy (14.5 lbs of extra weight over and above a normal backpack); (2) if the weight carried in the backpack has to be changed or the speed of the wearer changes significantly, then the springs (and/or spring placement) have to be modified, which is very difficult to accomplish in the field; (3) the efficiency of the generator is only 30-40%; (4) the electrical power generated, though much larger than other devices, is modest; and (5) the electricity is unusable in its present form for attaching a typical electronic device will overdamp the system and prevent sufficient movement of the load.
A next generation electricity generation backpack addressing these problems is desired. The present application is directed to such a backpack.